On 10/01/2018 06:12 PM, Ezequiel Garcia wrote: > On Mon, 2018-10-01 at 08:42 -0400, Nicolas Dufresne wrote: >> Hello Hans, >> >> Le lundi 01 octobre 2018 à 10:43 +0200, Hans Verkuil a écrit : >>> It turns out that we have both JPEG and Motion-JPEG pixel formats defined. >>> >>> Furthermore, some drivers support one, some the other and some both. >>> >>> These pixelformats both mean the same. >>> >>> I propose that we settle on JPEG (since it seems to be used most often) and >>> add JPEG support to those drivers that currently only use MJPEG. >> >> Thanks for looking into this. As per GStreamer code, I see 3 alias for >> JPEG. V4L2_PIX_FMT_MJPEG/JPEG/PJPG. I don't know the context, this code >> was written before I knew GStreamer existed. It's possible there is a >> subtle difference, I have never looked at it, but clearly all our JPEG >> decoder handle these as being the same. >> >> https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/sys/v4l2/gstv4l2object.c#n956 >> > > To add more data points on the gstreamer side, there's really no difference > between gstreamer's types image/jpeg and video/x-jpeg. > > Notably, jpegdec element just stuffs a huffman table if one is missing, > for any jpeg: > > https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/ext/jpeg/gstjpegdec.c#n584 lib/libv4lconvert/libv4lconvert.c also treats JPEG and MJPEG the same. It looks like JPEG and MJPEG are randomly used and I don't think you can assume that one will have a huffman table and not the other. Regards, Hans > >>> >>> We also need to update the V4L2_PIX_FMT_JPEG documentation since it just says >>> TBD: >>> >>> https://www.linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/pixfmt-compressed.html >>> >>> $ git grep -l V4L2_PIX_FMT_MJPEG >>> drivers/media/pci/meye/meye.c >>> drivers/media/pci/solo6x10/solo6x10-v4l2-enc.c >>> drivers/media/platform/sti/delta/delta-cfg.h >>> drivers/media/platform/sti/delta/delta-mjpeg-dec.c >>> drivers/media/usb/cpia2/cpia2_v4l.c >>> drivers/media/usb/go7007/go7007-driver.c >>> drivers/media/usb/go7007/go7007-fw.c >>> drivers/media/usb/go7007/go7007-v4l2.c >>> drivers/media/usb/s2255/s2255drv.c >>> drivers/media/usb/uvc/uvc_driver.c >>> drivers/staging/media/zoran/zoran_driver.c >>> drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c >>> drivers/usb/gadget/function/uvc_v4l2.c >>> >>> It looks like s2255 and cpia2 support both already, so that would leave >>> 8 drivers that need to be modified, uvc being the most important of the >>> lot. >>> >>> Any comments? >>> >>> Regards, >>> >>> Hans >> >> >
